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How To Make Tap Water Safe For Saltwater Aquarium?

how to make tap water safe for saltwater aquarium

If the thought of using tap water for saltwater tanks has crossed your mind, you aren’t alone. However, the only problem with tap water is the algae-promoting nutrients and chemical impurities it contains.

The best way to make tap water safe for saltwater aquariums is by purifying it using a RO/DI system. As a cheap alternative, you can treat tap water with a conditioner, but unfortunately, it doesn’t safeguard your reef tanks from nuisance algae.

Water is indeed the single most crucial component in any aquarium. You shouldn’t be filling up your saltwater aquarium or even performing water changes unless you’ve ensured your tap water is optimal and safe for your beloved aquatic pets.

Can You Use Tap Water In Saltwater Aquariums?

The water that comes from your sink is chemically treated for human consumption and not for the fish in your saltwater tank. Therefore, you should not use tap water directly from the faucet to fill your saltwater aquariums.

Downsides of Using Tap Water

Tap water contains ammonia, nitrates, chloramine, and other chemical compounds that can cause an imbalance in aquariums and adversely affect the health of the fish.

An overabundance of organic nutrients such as phosphorous and arsenic is another major issue with tap water. It can cause regular algae blooms and other water quality problems.

How To Make Tap Water Safe for Saltwater Aquariums?

If you want to make your tap water inhabitable for saltwater fish, there are mainly two ways you can do it:

Treating Tap Water With a Conditioner

You might have heard that treating tap water with a conditioner or dechlorinator makes it safe for the fish. But it’s not a full-proof method, and here is why.

A conditioner helps remove chlorine, chloramine, and heavy metals from the water. But, if your tap water contains solids and nutrients that are not covered by the conditioner, you will face algae blooms and water quality issues in the near future.

The amount of contaminants available in tap water is measured in TDS or total dissolved solids. TDS is a measurement unit for the dissolved inorganic salts and organic matter in the water column.

Keep in mind that if your tap water produces high TDS, you are going to have nuisance algae issues even if you are treating the water with a conditioner.

The quality of your tap water depends on where you live. City water contains an unpredictable mix of chemicals, which you can’t determine without testing the water for its chemical composition.

Another way is to reach out to your city’s local water treatment plant and enquire about their purification process, including the additives used.

Once you have the data for the chemical composition of your tap water, you can perform additional treatments and determine better ways to introduce it into your saltwater aquariums.

If you think it’s a lot of hassle, there is another way to make tap water safe for saltwater aquariums.

Purifying Tap Water Using RO/DI System

how to make tap water safe for saltwater aquarium

Investing in a RODI unit is probably the most reliable and convenient method to make tap water safe for your reef tanks.

RODI, or reverse osmosis deionization, is a water filtration system that removes contaminants commonly found in city water supplies.

Firstly, it filters out the dissolved solids in the water and then runs it through another set of filters to remove chemical compounds present in the tap water.

When using RODI water, you can be assured of the fact that the water going into your saltwater aquariums is of optimum quality and free from all sorts of contaminants harmful to your aquatic pets.

RO/DI system is hugely considered to be essential for reefing. Many hobbyists believe that it’s simply not possible to maintain a healthy, thriving saltwater aquarium without RODI water.
So, if you want absolute peace of mind over water quality and lay the foundations for a successful long-term saltwater tank, it will be worth investing in a RO/DI unit.

How to Choose the Best RO/DI System?

When you go out to buy a RO/DI filtration system for your reef tank, one of the most crucial selections you will have to make is the stages of filtration. It includes 4 stages system, 5 stages system, 6 stages system, and 7 stages system.

The different stages are filters – higher means more – that serve as additional membranes for water to pass through. A 4 stages filtration system includes a carbon block filter, sediment filter, DI resin filter, and an RO membrane.

Larger units or higher stages system comes with additional filters, usually including multi-stage resin and carbon block filters.

How Many Stages of RO/DI Filtration Do You Need?

Now, what is the best way to figure out how many RO/DI filtration stages you require for your saltwater aquarium?

We recommend choosing a system based on tap water conditions and demand for pure water production.

If you are a newbie, the best way for you is to get the water report of your local water supply. And reach out or call an expert at Spectrapure, BRS, or Marine depot and let them know your tap water TDS and chemical composition.

They should be able to guide you better and more accurately.

Most tap water ranges from 150 – 400 TDS based on where you live and whether you have a municipal supply or well water.

If you are aiming for 0 TDS, which is indeed a gold standard for reef tanks, you will need at least 4 stages RO/DI system. It should produce 0 TDS water in all water conditions and are best suitable for nano tank owners and those starting on a budget.

Do you know most reefers prefer 5 stages RO/DI system? Having it installed in your home means you don’t have to worry about the disinfectants your municipal water supply puts in the water.

Regardless of the water condition or where it comes from, the 5 stages RO/DI system will produce optimum quality water required for a thriving saltwater aquarium.

Lastly, when it comes to size or per-day filtering capacity, we recommend you buy as big as you can afford, even if you have a small aquarium. After all, who doesn’t want to produce water quickly?

Related Questions

Do you need RODI water for a saltwater tank?

Corals are sensitive little creatures that need extra tender loving care. RODI water is most favorable for them as it ensures no water quality issues and guarantees a stable, healthy, thriving saltwater/reef aquarium.

Can you use distilled water in saltwater aquariums?

Distilled water lacks minerals and nutrients required by marine life so preferably avoid using it in reef tanks.

In the case of dire emergencies, such as running out of RODI water, you can use distilled water to top up/top off but never as a primary source of water.

What is the difference between RO and RO/DI water?

An RO and RO/DI are almost identical but not the same. RO/DI system comes with an extra filtration stage called the “DI or Deionization”, which brings the water TDS to 0, making it ideal for reef aquariums.

RO systems are mainly used for residential purposes, such as producing drinking water that is suitable for freshwater aquariums as well. Whereas RO/DI systems produce 99.9% pure water best for scientific applications and use in saltwater aquariums.

How safe is dechlorinated tap water for saltwater aquariums?

With dechlorinated tap water, you may get away with chemical instability, but in the future, you’re likely to face nuisance algae blooms in your aquarium. The best way is to use RODI water and claim peace of mind from water quality issues.

Can you use RO water instead of RO/DI water in saltwater tanks?

Reverse osmosis (RO) water produces 10-20 TDS which is better than tap water but still not acceptable for reef tanks. If you want 0 TDS, you must use only RODI water for your saltwater setups.


To recap, you can make tap water safe for saltwater aquariums by treating it with a dechlorinator or purifying it via RO/DI.

We recommend installing a RO/DI unit as it produces the most favorable water for reef tanks. If your budget doesn’t allow you to go for RODI water, you can use a proper conditioner to make tap water inhabitable for your saltwater pets.

However, you may face some algae blooms in your aquarium, so be ready for it. To control the algae growing quickly in your tank, you must stay on top to prevent it from causing a nuisance.